The video I linked above is the only explanation I could find about how it actually works. He takes the thing out and it is an actual tuning fork at 440 Hz. You can use it as one. He claims it only resonates when A is played, which makes sense I guess.
Unless you use non standard tuning, then...
I posted a NGD about a week ago for G3166 that I could not resist. The guitar was very dirty. And one pod was lose. Today I finally had time to fix it. I just don't understand how some do not care to do any maintenance. I get strange enjoyment out of it. 😁
Remove knob and tighten the washer...